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S. Atag

Publications and source records attributed to S. Atag.

14 recordsLinked to original sources
arXiv2019

Substrate-limited helical edge states

We derived analytical results for the gapless edge states of two-dimensional topological insulators in the presence of electron-surface optical (SO) phonon interaction due to substrates. We followed an analytical algorithm, called Lee-Low-Pines variational approximation in the conventional polaron theory, to examine the substrate induced effects on both bulk and edge states of a two dimensional topological insulator within the frame work of Bernevig-Hughes-Zhang (BHZ) model. By implementing this algorithm, we propose a novel phonon-dressed BHZ Hamiltonian which allows one to investigate the effects of various substrates not only on bulk states but also on the associated gapless helical edge states (HESs). We found that both the bulk and HESs are significantly renormalized in the momentum space due to the substrate-related polaronic effects. The model we developed here clarifies which subtrates favor the HESs of quantum spin Hall system and which are not. Correspondingly, our work demonstrates that the substrate related polaronic effects have significant role on the emergence of HESs. In other words, we show that SO phonons due to substrates modify the electronic band topology of topological insulators together with the associated HESs and therefore they can be used to tune quantum phase transitions between topological insulators and non-topological ones.

cond-mat.mes-hall↗
arXiv2015

Prediction for CP Violation via Electric Dipole Moment of $\tau$ Lepton in ${\gamma\gamma \to \tau^{+}\tau^{-}}$ Process at CLIC

Pair production of tau leptons in two photon collision ${\gamma\gamma \to \tau^{+}\tau}^{-}$ is studied at CLIC to test CP violating QED couplings of tau leptons. CP violating effects are investigated using tau pair spin correlations which are observed through the hadronic decay of each $\tau$ into $\pi\nu$. Competitive bounds with previous works on the electric dipole moment from CP odd terms have been obtained.

hep-ph↗
arXiv2010

Extra dimensions in gamma gamma -> gamma gamma process at the CERN-LHC

Potential of the LHC to explore the phenomenology of the Kaluza-Klein (KK) tower of gravitons in the scenarios of the Arkani-Hamed, Dimopoulos and Dvali(ADD) model and Randall-Sundrum (RS) model is discussed via the process ${\gamma\gamma \to \gamma\gamma}$ including the Standard Model one loop diagram. The improved constraints on model parameters have been obtained compared to the LEP and Tevatron sensitivity.

hep-ph↗
arXiv2009

Extra dimensions in photon-induced two lepton final states at the CERN-LHC

We discuss the potential of the photon-induced two lepton final states at the LHC to explore the phenomenology of the Kaluza-Klein (KK) tower of gravitons in the scenarios of the Arkani-Hamed, Dimopoulos and Dvali(ADD) model and Randall-Sundrum (RS) model. The sensitivity to model parameters can be improved compared to the present LEP or Tevatron sensitivity.

hep-ph↗
arXiv2007

Anomalous Quartic $WWγγ$ and $ZZγγ$ Couplings in $eγ$ Collision With Initial Beams and Final State Polarizations

The constraints on the anomalous quartic $WWγγ$ and $ZZγγ$ gauge boson couplings are investigated through the processes $eγ\to W^{-}γν_{e}$ and $eγ\to Zγe$. Considering the longitudinal and transverse polarization states of the final W or Z boson and incoming beam polarizations we find 95% confidence level limits on the anomalous coupling parameters $a_{0}$ and $a_{c}$ with an integrated luminosity of 500 $fb^{-1}$ and $\sqrt{s}$=0.5, 1 TeV energies. Assuming the $W^{+}W^{-}γγ$ couplings are independent of the $ZZγγ$ couplings we show that the longitudinal polarization state of the final gauge boson improves the sensitivity to anomalous couplings by a factor of 2-3 depending on energy and coupling. An extra enhancement in sensitivity by a factor of 1.3 comes from a set of initial beam polarizations.

hep-ph↗
arXiv2004

$ZZγ$ and $Zγγ$ couplings at linear $e^{+} e^{-}$ collider energies with the effects of Z polarization and initial state radiation

The constraints on the neutral gauge boson couplings, $ZZγ$ and $Zγγ$, are investigated at linear $e^{+}e^{-}$ collider energies through the $Zγ$ production with longitudinal and transverse polarization states of the final Z boson. Because of high energy of linear electron- positron beams, initial state radiation (ISR) considerably changes the production cross section. We obtain an increase in the cross section by a factor of 2-3 due to ISR for transverse polarization and by a factor of 10-100 for longitudinal polarization states depending on the energy. We find the 95% C.L. limits on the CP conserving form factors $h_{3}^{Z}$, $h_{4}^{Z}$, $h_{3}^γ$ and $h_{4}^γ$ with integrated luminosity 500$fb^{-1}$ and $\sqrt{s}=$0.5, 1, 1.5 TeV energies. It is shown that the longitudinal polarization of the Z boson, together with ISR, can improve sensitivities by factors 2-3.

hep-ph↗
arXiv2004

Top Quark Spin Polarization in ep Collision

We discuss the degree of spin polarization of single top quarks produced via $Wg$ fusion process in $ep$ collision at TESLA+HERAp and CLIC+LHC energies $\sqrt{s}=1.6$ and 5.3 TeV. For $eb \to t \barν$ subprocess we show that the top quark spin is completely polarized when the spin basis is chosen in the direction of the incoming positron beam in the rest frame of top quark. A description on how to combine the cross sections of $e^{+}b\to t\barν$ and $e^{+}g\to t\bar{b}\barν$ processes is given. $e^{+}$-beam direction is taken to be the favorite top quark spin decomposition axis in its rest frame and it is found to be comparable with the ones in $pp$ collision. It is argued that theoretical simplicity and experimental clearness are the advantage of $ep$ collision.

hep-ph↗
arXiv2003

Top quark spin in ep collision

We discuss the degree of spin polarization of single top quarks produced via $Wg$ fusion process in $ep$ collision at TESLA+HERAp and CLIC+LHC energies $\sqrt{s}=1.6$ and 5.3 TeV. A description on how to combine the cross sections of $e^{+}b\to t\barν$ and $e^{+}g\to t\bar{b}\barν$ processes is given. $e^{+}$-beam direction is taken to be the favorite top quark spin decomposition axis in its rest frame and it is found to be comparable with the ones in $pp$ collision. It is argued that theoretical simplicity and experimental clearness are the advantage of $ep$ collision.

hep-ph↗
arXiv2003

$ZZγ$ and $Zγγ$ couplings in $γe$ collision with polarized beams

The potential of $γ$e mode of linear $e^{+}e^{-}$ collider to probe $ZZγ$ and $Zγγ$ vertices is investigated through the Z boson production from the procees $γe\to Z e$. Considering the longitudinal and transverse polarization states of the Z boson and incoming polarized beams we find the 95% C.L. limits on the form factors $h_{3}^{Z}$, $h_{4}^{Z}$, $h_{3}^γ$ and $h_{4}^γ$ with integrated luminosity 500$fb^{-1}$ and $\sqrt{s}=$0.5, 1, 1.5 TeV energies. It is shown that the polarization can improve sensitivities by factors 2-3 depending on the energy.

hep-ph↗
arXiv2001

Anomalous Wtb Coupling in ep Collision

The potential of ep collision to prospect for anomalous Wtb vertex is discussed from the single top quark production process $ep\to t\barν+X$ for TESLA+HERAp and CLIC+LHC energies. Sensitivities to anomalous couplings $F_{2L}$ and $F_{2R}$, in the case of CLIC+LHC, are shown to be comparable with LHC.

hep-ph↗
arXiv2000

Anomalous WW-Gamma Vertex in Gamma-p Collision

The potential of LC+HERAp based Gamma-p collider to probe WW-Gamma vertex is presented through the discussion of sensitivity to anomalous couplings and P_T distribution of the final quark. The limits of -0.04<Δκ<0.04 and -0.11<λ<0.11 at 95% C.L. can be reached with integrated luminosity 200(1/pb). The limit for Δκis comparable to one which is expected from LHC. The bounds are also obtained from corresponding ep collider using Weizsacker-Williams Approximation to compare with real photons.

hep-ph↗
arXiv1999

Anomalous WW-gamma Vertex at LC+HERA Based gamma-p Collider

The potential of LC+HERA based gamma-p collider to probe WW-gamma vertex is presented through the discussion of sensitivity to anomalous couplings and p_{T} distribution of the final quark. The limits of -0.16<(kappa-1)<0.14, -0.30<lambda<0.30, at 95% C.L. can be reached with integrated luminosity 100pb^{-1} and they are competitive to projected future limits from other colliders. The results are compared with corresponding ep collider using Weizsacker-Williams Approximation.

hep-ph↗